Catalytic dehydrogenation of isopropylbenzene



Patented Feb. '29,

. UNITED STATES PATENT OFFICE amass CATALYTIC DEHYDBOGENATION OF ISOPROPYLBENZENE Herbert Mnggleton Stanley, Tadworth, and Fran-i cis Edward Salt,

Banstead, England, assignors to The Distillers Company Limited, Edinburgh, Scotland, a British-company:

No Dtawlng. AppllcationMay12,1942,SerlalNo. maze In Great Britain May z, 1941,

4 Claims. ('01. 260668) In British Patent No. antennae is described a process for the'dehydrog'ena'tion-oi isopropylbenzene to alphamethylstyrene in the presence of a vanadium oxide supported catalyst at elevated temperatures. A statement is also made therein to the eilect that the presence of water vapour as a diluent reduces the eillciency of the It has now been found that, although the presenceof water vapour (e. g. steam) in the reacting gases does reduce somewhat the degree of reaction at any given temperature, nevertheless, by operating at slightly higher temperatures, a. satisfactory dehydrogenation can be carried out in the presence of vanadium oxide catalysts. l

According to the present invention, a process for .the catalytic dehydrogenation of isopropylbenzene comprises passing isopropyibenzene in admixture with water vapour over an oxideof vanadium at a temperature between 500 and by weight of vanadium pentoxide is very satisfactory.v Other oxide catalystsvare less satisfactory since they are much more sensitive to the presence of steamthan isthe vanadium.

oxide catalyst. Thus. zinc oxide and cerium oxide on activated alumina are ,fairly active catalysts for the dehydrogenation oiisopropylbenzene, but their catalytic activities are almost entirely suppressed by the presence of substan ent, than in the absence of steam. some indication of the mechanism of the action of steam is aiforded by the observation that the gaseous products of dehydrogenation in the presence of excess of steam contain certain proportions of oxides of carbon. This is believed to be due to the reaction between the steam and any carbon deposited on the catalyst surface. hereby the carbon becomes converted into ,oxides of carbon, and is thereby removed from' the catalyst surface. Whatever be the exact mechanism, the practical eifect of the use of steam is to prolong the period of useful activity oi the catalyst between reviviiications from 6 to 10 hours (in the absence of steam) to 50. hours or more when operating in accordance with this inventionwhen excess steam is used. This is very desirable from an industrial standpoint;

" The'catalyst-used in the process is; preferably vanadium pentoxide supported on activated almnina granules. or similarly relatively inert supportmaterial. A catalyst prepared by impregnating activated alumina granules with 5% by weight and after a continuous period of operationeof 50- hours, it was still maintained at about 88% hydrogen anda residue of. oxidbs'oi tlal amounts of watervapour. Cataly taining the oxides of molybdenum and tungsten occupy an intermediate position between zinc oxide and vanadium oxide with respect to their sensitivity tothe presence of water vapour.

The dehydrogenation can be carried out at temperatures of 500-700' 0., preferably at about 560-600 C. in tubular reactors which are extemally'heated to supply the heat necessary to.

support the highly endothermic} dehydrogenation reaction. Alternatively, the reaction, can becarried out in a multi-stage unit with interstage preheating.

The proportion of steam employed maybe varied within certain limits, but should be preferably 8 or more mols. of steam per mol. of isopropylbenzene fed to the reactor.

Example I Amlxture of steam and isopropylbenzene vapour in the molar ratio of 3.5 mols. of steam to 1 mol. of isopropylbensene was passed over a.

catalyst formed by impregnating activated alumina with 5% by weight of vanadium pentoxide. The catalyst was contained in a l" internal diameter heat-resisting metal tube heated in a tubular electric-furnace to a temperature oiv about 580 C. as measured by a pyrometer in the' furnace annulus. The liquor feed .rate corresponded to. 425 cc./hour of isop'ropylbenzene per litre of catalyst.

Under these conditions, the initial percentage decomposition of the isopropylbenaene was 27.0%

practically the same level. The crude liquid condensate contained 25.8% by weight of alpha-- methylstyrene, and practically no styrene,-while the gaseous products of reaction consisted oi carbon and methane. A balance over-the-whole run indicates that the decompositionsif-JOO mols;

ci isopropylbenzene yielded 89 mols. of alphamethylstyrene, mols. oi oi oxides of carbon.

sts conhydrogen and 8 mols. 1 Whendecomposition s effected in theab sence sition per passtell from 30% to 24% in 9 hours.

Example 11 Equimolecular proportions of steam and isopropylbenzene were passed over the same catalyst as used in Example I at 580 C. and at a teed rate of 970 cc./hour of liquid isopropylbenzene per litre oi. catalyst. The percentage de composition per pass tell gradually from 25.0% to 20.0% by weight after 24 hours of continuous operation. Thebulked crude condensate contained 21.5% by weight of alpha-methylstyrene, no detectable amounts of styrene, and only traces of high-boiling products. For every 100 mols. of isopropylbenzene decomposed, approximately 92 ,mols. of alpha-methylstyrene were recovered. The gaseous reaction product contained 87.4%

ascaoso by .volume hydrocen and 1.2% by volume methane, the residue consisting oi oxides of carton and small amounts of oletins.

Whatwe claimis: w

l. A process for the catalytic dehydrogenation of isopropylbenzene which comprises passing isopropylbenzene in admixture with at least one molecular proportion of steam to each molecular proportion of isopropylbenune over an oxide 01 vanadium at a temperature between 500 C. and 700 C.

2. A process accordina to claim 1 wherein the catalyst is vanadium pentoxide supported on a substantially inert support material.

3. A process accordinl to claim 1 wherein the dehydrogenation is elected at a temperature between about 560 and about 800 C.

- 4. A process according to claim 1 wherein the molar proportion of steam to isopropylbenzene is at least three to one."

T MUGGLETON STANLEY. FRANCIS EDWARD SALT. 

